Regulation of intestinal cell growth and the loss of that regulation during malignant transformation of cells involves a complex series of molecular events. Our objective is to determine the role of pp60c-scr and related protein-tyrosine kinases in this regulatory process. Historically, a strong correlation exists between elevated pp60src kinase activity and cell transformation. We determined that pp60c-src isolated from human colon carcinomas, malignant colonic polyps, and benign polyps at greatest risk for developing cancer, has higher specific activity than pp60c-src from normal mucosa. Our results also show that pp60c-src activity decreases as primary cells differentiate along the crypt-villus axis of chicken intestine. Together, the data suggest that down-regulation of c-src is important for differentiation, and deregulation of c-src is important for transformation of intestinal epithelia. We will study mechanisms that regulate pp60c-src activity in intestinal cells. We, and others, have identified three mechanisms that regulate pp60c-src activity in other cells: phosphorylation of pp60c-src, association of pp60c-src with another protein, or mutation within the coding region of c-src. Posttranslational events that are known to alter pp60c-src activity will be studied in cells along the crypt-villus axis of chicken intestine. c-src will be isolated from colon carcinomas which have elevated pp60c-src activity, and its coding region will be analyzed for somatic mutations and tested for oncogenic potential in fibroblasts. pp60c-src activity will be measured in colonic mucosa of patients with ulcerative colitis which, like adenomatous polyps, has malignant potential. Finally, the activity of pp60c-src -related tyrosine kinases will be measured and the substrates of tyrosine kinases will be identified in colon carcinoma cells. Our aim is to understand the role of pp60c-src and related kinases in regulating growth of intestinal cells. By addressing basic mechanisms of growth control in normal cells, we can elucidate pathogenic mechanisms in human disease, namely, colonic carcinogenesis. We hope to identify early events that perturb normal regulatory pathways in the precancerous mucosa of colonic polyps and ulcerative colitis. The results will impact on prevention, diagnosis and treatment of colon cancer.